Field of the Invention
The present invention relates to an apparatus for and a method of observing cells.
Description of the Background Art
For observation of cells cultivated in a culture vessel, it is necessary to find a focal position suitable for the observation of the cells. It has been hitherto known to perform what is called “z-stack imaging” or “bracketing imaging” that is a technique of acquiring a plurality of images using varied focal positions for the purpose of detecting an in-focus position for the cells in the culture vessel. The z-stack imaging is disclosed, for example, in Japanese Patent Application Laid-Open No. 2015-82096 (paragraph 0019).
The in-focus position is estimated, for example, by determining the variance value of pixel values of z-stack images. Unfortunately, the variance value changes rapidly near the in-focus position. For accurate estimation of the in-focus position, it is necessary to shorten imaging intervals. That is, the greater the number of z-stack images is, the more accurately the in-focus position is estimated. However, the greater number of images taken for z-stack imaging causes illuminating light to do greater damage to the cells because the cells are irradiated with the illuminating light during the imaging. For suitable observation of the cells with minimum damage to the cells, it is necessary to accurately estimate the in-focus position with high precision from a smaller number of images taken for z-stack imaging.